Rheostat



No. v6|5,4|9. Patented Dec. 6, |898.

" C. WIRT.

nHEosrAT.

(Applicntiqn lsd.4 July 26, 1897.) (lo Model.)

3 Shaacs--Sheet I.

WITNESSES: INVENTOR:

PHoTmLlYHo.. WASHINGTON. o. c.

me mams PETERS Co.

No. 6|5 ,4|'9. Patented Dec. 6, |898.

C. WIBT.

RHEOSTAT.

(Application lod July 2B, 1807.) (In Model.)

3 Shasta-Sheet 2.

C' AX .B Ax bz WlTNESSESL `INVENTOFx: l :y CAW/7155 )YI/YT',

Y u. n. c.

TH: Nomus Patins op. Pngroumo., wAwmmo No. 6|5,4|9. Patented Dec. 6, |898.

C. WIRT.

RHEUSTAT.

(Applicltion Bled July 26, 1897.)

3 Shasta-Shut 3.

FIG'. 10. .A a6

- WITNES ES:

UNITED STATES PATENT OFFICE.

CHARLES VIRT, OF PHILADELPHIA, PENNSYLVANIA.

RH EOSTAT.

SPECIFICATION forming part of Letters Patent No. 615,419, dated December 6, 1898. Application filed July 26, 1897.4 Serial Nox M6037. (No model.)

To all whom, it may concern.-

Beit known that LOHARLES WIRT, of Philadelphia, in the Sta-te of Pennsylvania, have invented certain neur and useful Improvements in Rheostats, whereof the following is a speciiication, reference being had to the accompanying drawings.

My invention relates to rheostats adapted for the control of currents of large amperage and to that class of such devices wherein a conductor consisting of a strip of material folded upon itself and suitablyinsulated comprises the path of `electrical resistance'. As ordinarily constructed said folded conductor is separate from the commutating device by which the effective resistance of the rheostat is changed, said conductor being subdivided and placed in circuit with the commutating device by means of wiring connections.

It is the object of my present invention, iirst, to lessen the cost of construction of a rheostat by dispensing with a commutator, and, second, to use a single continuous conductor for the path of electrical resistance, dispensing with wire connections and joints.

Aside from the consequent lessening of the cost of construction, the second feature above mentioned is valuable for the reason that failures in the ordinary forms of rheostats often occur at said joints.

Broadly speaking, my invention comprises a casing adapted to resist a high temperature, a continuous strip of conducting material folded and fixed within said casing, a movable contact member mounted upon said casing, and means to shift said contact member in direct electrical contact with the successive folds of said conductor. The various parts enumerated are so arranged that said contact member serves to short-circuit or otherwise cut out a part of said conductor, and thus alter the effective resistance of the device as a whole.

My invention also comprises certain novel features of construction, such as means to prevent creeping of the folded conductor Within the casing, means for keeping down the temperature of that portion of the conductor traversed by the movable contact, and means for obtaining a double contact upon opposite sides of said-conductor, as hereinafter described.

4, section being taken on the line 5 5 in said figure. Fig. 6 is a sectional view of the device shown in Figs. +L and 5, section being taken on the line 6 6 in Fig. 4. Fig. 7 is a perspective view of a detail of the device shown in Figs. 4, 5, and 6. Fig. 8 is a plan view of a modified form of my invention. Fig. 9 is a sectional view of the device shown in Fig. 8, section being taken on the line 9 9 in said figure. Figs. l0, ll, l2, and 13 show modifications in the details of construction.

Similar letters indicate corresponding parts in the several figures.

Referring to the form of my invention shown in Figs. l, 2, and 3, A A are plates of metal connected by screws a, provided with nuts ax, said screws being passed through side pieces a a2. Said plates and side pieces form a casing for the folded conductor B.

The conductor B consists of a continuous length of metallic ribbon folded upon itself, as indicated in Fig. l, the terminal folds B B2 of said conductor being respectivelyin electrical contact with the terminal pieces C C'.

The conductor B, which forms the path of electrical resistance aforesaid, is mounted in the casing, so as to be separated therefrom by a layer of insulating material AX, except at its extremity B2, the terminal piece C in contact with said extremity being also in contact with the side piece a. The terminal piece C being thus in electrical connection with the casing, a shunt connection is made from the end B of the conductor B through said terminal piece C and the casing-plate A to a contact-lever D, pivotally mounted upon the casing-plates A A, as indicated at d d. The forward end of said lever Dis conveniently provided with an insulating-han dle D3.

Slots a3 a3, concentric with the pivot of the lever D, extend through the opposed plates A A and through the layers of insulating ma- IOO terial A to the opposite surfaces bf the folded conductor B. In this form the lever D is composed of resilient material and is provided with contact members D D, which are entered in said slots a3 as, pressing directly upon the opposite surfaces of the folded conductor B, asindicated by the arrows in Fig. 2.

Certain portions of the conductor B extending beneath the slots a3 a3 are provided with contact-pieces B2, which are inserted between alternate adjoining folds, as indicated in Fig. 3. Said contact-pieces insure a good surface of contact for the spring contact members D D', reducing the local resistance, thus preventing undue heating of the conductor-folds at the portions traversed by said members. The bights of the conductor B which inclose said contact-pieces B2 are separated from each other by the insulating material 29X.

It is obvious that if the device above described is connected in the circuit at t by means of the terminal screws c c a minimum resistance will be offered to the passage of a current through the said circuit when the contactlever D is swung to the extremity of the slots a into direct contact with the terminal piece C, (see Fig. 1,) for the reason that in said position the lever D, being in shunt connection, as above described, serves to short-circuit the current from one to the other of said terminal pieces C C. It is also obvious that as said contact-lever is shifted in the direction of the arrow 'upon Fig. l said lever D short-circuits a successively-lessening number of said folds until in its extreme movement in said direction it is brought into contact with the terminal piece C, and the current in the circuit X is compelled to fol low the entire length of the folded conductor B.

The form of my invention just described may be advantageously used in exposed positions; but for cheapness of construction the form illustrated in Fifrs. fl, 5, G, and 7 is preferable. In the latter form the lever D is rigid, and the contact member D, being provided with a spring CZK, bears upon the folds of the conductor B which protrude beyond thc edge of the casing-plates A A.

.As indicated in Fig. 4, the alternate bights of the conductor B at the contact ends of the folds are formed some distance within the casing-plates A A, and in the space thus provided eontact-pieces B2 and insulating-pieces b2 are inserted for the purpose above set forth. In this form of my device the side pieces Ct', which serve to confine the conductor B, are made integral with the plates A A, as indicated in Fig. (5.

In the form shown in Figs. 8 and l) the plates A A of the casing consist of slabs of insulating material, such as slate, so that the insulating material A is dispensed with. In the latter form the terminal pieces C C form the sides of the casing and serve to confine the folded conductor B, the screws a a, passing directly through the terminal pieces C C', being secured by nuts a upon their lower extremities.

As indicated in Fig. 0, the lever D is pivoted upon a stud cl', secured to the upper plate A by means of screws d2 passing through the latter. The lever D is electrically connected with the terminal piece C, as indicated at D2.

A convenient construction to prevent creeping of the conductor B during its contract-ion and expansion is illustrated in Fig. 2. In said form the folded conductor B is struck up in a line across its plane, and the humps 1)/ upon the individual folds of said conductor are engaged by a corresponding groove a4 and a ridge a5 upon the upper and lower plates A A, respectively.

In the forms shown in Figs. l0 and l1 the folded conductor B is not struck up, as above described, but the insulating-pieces 12X are provided with lugs b3, which are entered in grooves a in the respective plates A A. In said form the insulating-pieces hx serve to rctain the folded conductor B in proper position by frictional contact with the latter, the lugs h3 bB being of course in fixed relation with the casing-plates A A.

As indicated in Fig. l2, the eontaetpieces B2 and insulating-pieces b2, described in con nection with the form illustrated in Figs. 4, 5, and G, may be bent laterally, as indicated at b4 in Fig. 12, the engagement of said lateral bends with similar bends in conductor B serving to prevent the aforesaid creeping ac tion of the conductor B.

As indicated in Fig. 13, the conductor may be thus bent laterally together with the insulating-pieces hx, the interlocking engagement of the bends in the respective folds serving the same end.

I prefer to construct my invention, as above described, with the lever D in shunt connection with one extremity of the folded conductor B. It is, however, obvious that said shunt connection may be omitted and the lever D directly connected with the exterior circuit X..

Itis obvious that various modifications muy be made in the details of construction of my invention without departing from its essential l features. I therefore do not desire to limit myself to the precise embodiment thereof which I have shown and described.

l. In a rheostat the combination with a,

IOS

TIO

ela/rie able Contact member mounted upon said casing, and means to shift said member in direct contact with the portions of the successive folds of said conductor, provided with the said intermediate fixed contact-pieces, Substantially as set forth.

In a rheostat the combination with a casing, of a continuous strip of electrical conducting material, folded Within said casing, a contact-lever pivoted upon said casing, a slot in said casing concentric with the pivot of said lever, a contact member upon said lever entered in said slot, in direct contact with the strip of conducting material, and means to shift said member in direct contact with Witnesses:

A. E. PAIGE, E. L. FULLERTON. 

